Concat MKVs; great differences in size with ffmpeg and MKVToolNIX

2017-06-17 22:18:37

Hello,

sorry if this subforum is not the right place...I have concatenated 3 MKVs with ffmpeg as well as with MKVToolNIX and the sizes of the resulting concatenated files differ greatly, though the content is identical.Where does this difference come from, does MKV have so much overhead?

The three MKVs have these sizes: 36MB, 31MB and 56MBConcatenation with ffmpeg:

--- Output of job 'Multiplexing to file "title06 (1).mkv" in directory "/Users/mn/work"' started on 2017-06-19 22:22:14 ---mkvmerge v11.0.0 ('Alive') 64bit'/Users/mn/work/title06.mkv': Using the demultiplexer for the format 'Matroska'.'/Users/mn/work/title07.mkv': Using the demultiplexer for the format 'Matroska'.'/Users/mn/work/title08.mkv': Using the demultiplexer for the format 'Matroska'.'/Users/mn/work/title06.mkv' track 0: Using the output module for the format 'MPEG-1/2'.'/Users/mn/work/title06.mkv' track 1: Using the output module for the format 'AC-3'.'/Users/mn/work/title07.mkv' track 0: Using the output module for the format 'MPEG-1/2'.'/Users/mn/work/title07.mkv' track 1: Using the output module for the format 'AC-3'.'/Users/mn/work/title08.mkv' track 0: Using the output module for the format 'MPEG-1/2'.'/Users/mn/work/title08.mkv' track 1: Using the output module for the format 'AC-3'.The file '/Users/mn/work/title06 (1).mkv' has been opened for writing.Appending track 1 from file no. 1 ('/Users/mn/work/title07.mkv') to track 1 from file no. 0 ('/Users/mn/work/title06.mkv').Appending track 0 from file no. 1 ('/Users/mn/work/title07.mkv') to track 0 from file no. 0 ('/Users/mn/work/title06.mkv').Appending track 0 from file no. 2 ('/Users/mn/work/title08.mkv') to track 0 from file no. 1 ('/Users/mn/work/title07.mkv').Appending track 1 from file no. 2 ('/Users/mn/work/title08.mkv') to track 1 from file no. 1 ('/Users/mn/work/title07.mkv').The cue entries (the index) are being written...Multiplexing took 1 second.

There is a difference in the two ffprobe outputs:For the MKVToolNIX concatenated file ffprobe says "bitrate: 3021 kb/s" and for the ffmpeg concatenated file "bitrate: 4696 kb/s".I haven't noticed this earlier, and to be honest I have no idea what it means (what is this value compared to the "4500 kb/s" in the stream?)Regarding the duration of the concatenation (1s), I doubt that the video streams were reencoded on my Macbook Pro Late 2011...